Hello Ahmad,
On 31.01.24 18:21, Ahmad Fatoum wrote:
On 31.01.24 17:57, Stefan Kerkmann wrote:
OOB writes can be triggered when fdt->dt_size * 2 is still smaller than
the property for which memory should be allocated. This can happen under
rare circumstances when editing a fdt with the of_property command and a
property is larger than 128k in size.
This happend when editing a FIT image (which is a ftd) with the
of_property command and the Kernel image was around 8M in size.
The simplified call chain is the following:
of_property -> of_flatten_dtb -> create new fdt with 64k in size (this is
fixed) -> __of_flatten_dtb -> attempt to copy kernel image (8M) ->
fdt_ensure_space -> allocate only 128k for fdt->dt -> memcopy 8M into fdt->dt
buffer -> crash
The fix is to grow fdt->dt to hold at least the new property. The power
of 2 increment is untouched to keep the same behaviour otherwise.
Signed-off-by: Stefan Kerkmann <s.kerkmann@xxxxxxxxxxxxxx>
---
drivers/of/fdt.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index 4f79a6120f..1f24ed0bbc 100644
--- a/drivers/of/fdt.c
+++ b/drivers/of/fdt.c
@@ -399,6 +399,10 @@ static int fdt_ensure_space(struct fdt *fdt, int dtsize)
previous = fdt->dt;
new_size = fdt->dt_size * 2;
+ while (new_size <= dtsize) {
+ new_size *= 2;
+ }
A nitpick that I solely note because I already had feedback on the first patch:
Kernel coding style is to omit { braces } for single statement blocks.
In your case you could just do:
if (new_size <= dtsize)
new_size = roundup_pow_of_two(new_size + dtsize);
I think to skip the loop.
Thanks! That is the better solution.
To not over provision memory I changed the new size to be
`roundup_pow_of_two(fdt->dt_size + dtsize)` as we know for sure that
`dtsize` is already larger than `fdt->dt_size * 2`.
In (made up) case that we already have 8k space for the fdt and got a
17k property we would allocate 65k (8k + 8k + 17k = 33k ⇾ rounded ⇾ 65k)
and only 32k (8k + 17k = 25k → rounded → 32k) with `fdt->dt_size + dtsize`.
Cheers,
Ahmad
+
if ((fdt->dt = memalign_realloc(previous, fdt->dt_size,
new_size)) == NULL) {
free(previous);
Cheers
Stefan
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